Is it possible to cheat in backgammon? I believe so.
Have you ever seen a magician, either on TV or live? They can do amazing
things. They practice trickery. It is scary to think about what they can
do.
I know a guy who has a very smooth motion. He rolls the dice out of the cup
and leaves his hand just over the spot where the dice will land.
Immediately after the dice land he can smoothly and imperceptibly barely
touch one of the dice to move it to a different number.
Some people use a magnet and dice that have metalic matter attracted by the
magnet.
Some people use the "dump shot," where a die is placed in the cup and then
they slide it out of the cup instead of rolling it.
Some people have a set of dice with faces numbered 4-5-6-4-5-6. They can
switch to these dice in a race and switch back to the honest dice without
your ever knowing about it.
Some people hold one die out of the cup in the crook of the little finger.
They roll one die out of the cup and smoothly place the other die of the
board.
Some people are able to move a checker from one spot to another without
your seeing it.
In Los Angeles in the 1980s there were three famous dice mechanics. One guy
practiced his technique in his garage for hundreds of hours and was able to
hit any direct shot at will.
As far as I know, the USA tournament scene today is clean, free from dice
mechanics.